While every attack can’t be prevented, we have to learn from each failure

It is a hard truth that law enforcement and U.S. intelligence services cannot thwart every terrorist attack, and certainly not mass murders committed by individuals who are not only prepared, but eager, to die in exchange for the deranged pleasure of killing innocent, anonymous others.

But that doesn’t mean it isn’t important to try, and with the murders Thursday in Tennessee by Mohammod Youssuf Abudlazeez, government investigators need to comb through the evidence to see if, and how, this bloodthirsty 24-year-old went undetected. Almost certainly, there will be painful lessons to learn.

Abudlazeez killed four Marines in a shooting rampage at two military recruiting centers in Chattanooga. He was also killed. Three of the victims were veterans of Iraq or Afghanistan, or both. The fourth was a 21-year-old who had just finished boot camp. Three others were injured.

In hindsight, clues are already appearing, though it is far from clear that they, alone, should have set off alarms. First, Abudlazeez’s father had been investigated several years ago for giving money to an organization thought to have ties to terrorism. At one point, the father was on a terrorist watch list and was questioned while abroad. He was later removed from that list.

Abudlazeez was born in Kuwait and became a naturalized U.S. citizen. On Friday, it was revealed that he spent seven months in Jordan last year. Investigators are trying to determine if he had been in contact with any extremist groups before or during that trip.

Lacking any indication that Abudlazeez suffered some kind of mental illness, though, it seems likely that he was acting as a lone-wolf terrorist in service of some violent cause. To be able to hide those inclinations so well that they could go broadly undetected seems unlikely, though something similar happened with the Tsarnaev brothers in the Boston Marathon bombing two years ago.

That is one of the prime issues that investigators need to probe. Where did Abudlazeez leave footprints that might have tipped off friends or authorities had they noticed them? Who else did he associate with who might have similar murderous intentions? Under what circumstances was he able to acquire the weapons that he used?

The killings also count as an uneasy sign, given that ISIS and other terrorist groups are seeking to foment lone-wolf attacks in this country. Only two months ago, two gunmen attacked an anti-Islamic event in Dallas. That attack failed and both gunmen were killed.

Of course, while the United States rightly worries about terror attacks by radicalized Muslims, the country also grows its own terrorists. Dylann Roof is surely one of those. He is charged with murdering nine African-Americans in Charleston, S.C., in the twisted and ludicrous hope of inciting a race war.

Terrorism is, at its root, a form of crime and we know better than to think all crime can be prevented. But it can be diminished through wise social programs and effective policing techniques.

So, too, can terrorism be diminished. The United States has done remarkable work in detecting and preventing attacks, including a potentially devastating one on the New York City subway system. There have been many other successes.

While it is impossible to stop every attack, that has to be the goal, unreachable though it is. That’s the approach that encourages law enforcement and intelligence agencies to continue honing their skills, and digging ever deeper into the dark recesses of the minds of men such as Mohammod Youssuf Abudlazeez.